The present invention relates generally to the smelting of iron oxides by processes that generate an offgas effluent that has a sulfuric content. More particularly, the invention concerns a method of reducing the sulfuric content in such an offgas. The method has particular utility in smelting processes using iron ores and iron-bearing oxides such as steel plant dusts and sludge. The Government of the United States of America has rights in this invention, pursuant to Cooperative Agreement No. DE-FC07-94ID13284, awarded by the U.S. Department of Energy.
Methods of smelting iron using iron ore pellets and coal-based fuels are well known in the art. During the smelting process, however, a substantial amount of sulfur is released in the offgas effluent. The sulfur present within the offgas originates from the sulfur contained in the iron oxide and coal charged to the smelter reactor. The sulfur usually is present in the iron oxide or coal in one or more of the following chemical forms: calcium sulfide, calcium sulfate, manganese sulfide, manganese sulfate, iron sulfide, iron sulfate, and organic compounds containing sulfur. In the offgas the sulfur typically is present in one or more of the following chemical forms: hydrogen sulfide, carbon oxysulfide, sulfur dioxide, and carbon disulfide. Traditionally, the sulfuric level in the offgas has been reduced by incorporating conventional gas desulfurization equipment into the process. However, current gas desulfurization equipment involves the use of lime (CaO), or redox equilibria, which require expensive equipment. Moreover, the desulfurization equipment has high operating costs.
Generally, the high sulfur levels present in steel plant effluent must be lowered prior to reaching the environment. However, the use of conventional equipment to reduce sulfur levels deleteriously affects iron smelting process costs. Accordingly, it is an object of the invention to produce an economical method of iron smelting that minimizes the environmental impact.